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Noclevername
2013-Dec-05, 04:37 AM
Now, I'm not talking about its moons (http://cosmoquest.org/forum/showthread.php?147749-Ice-is-nice-but-Water-is-wetter), but the inside of the planet Neptune and its poor cousin, Uranus. Both are considered to be "ice giants" because they are thought to contain vast quantities of H2O and other volatiles.

Now from my layman's understanding, the ice under those massive pressures is not frozen at all, but some kind of ultra-dense hot super-ice. And I am given to believe that there may be some kind of ultra-dense super-water may also exist at certain depths within those worlds. Given there's liquid (of a sort), and ammonia and methane in its mix which can form complex carbon compounds given the right circumstances, plus a surplus of heat energy, I can imagine with my colorful mind life, in some of its glory, developing within those unlit fluid layers.

Now pick the idea apart. Tell me what obstacles stand in the way of Ice Giant Whalesong. Tear into my imaginary Neptunian fishies, and leave nothing standing ...er, swimming... in your wake, down to the tiniest microbe.

Selfsim
2013-Dec-05, 05:19 AM
... I can imagine with my colorful mind life, in some of its glory, developing within those unlit fluid layers.

Now pick the idea apart. Well, Ok .. (if you insist) ...

... I think the problem starts with not fully appreciating the fact that the only life we know of, only exists here on Earth .. not Neptune.

... There ... that should sort it all out! :p :)

Cheers

Noclevername
2013-Dec-05, 05:24 AM
Well, Ok .. (if you insist) ...

... I think the problem starts with not fully appreciating the fact that the only life we know of, only exists here on Earth .. not Neptune.

... There ... that should sort it all out! :p :)

Cheers


You're not even trying anymore.

Noclevername
2013-Dec-05, 08:03 AM
If "they might not be there" is really the best thing you can come up with, I'm going to be very disappointed.

TheBrett
2013-Dec-05, 08:34 AM
I guess it could happen, if it was in an area that was stable enough for life to emerge from that particular brew. If I remember right, there used to be proposals that some type of life could emerge in Jupiter's atmosphere, but that mostly faded away because we discovered weather patterns that sucked parts of the atmosphere down deep - the kind of change that would kill just about any life we would recognize.

Neptunian life would be awesome. Pity it would be super-hard to actually identify it.

Selfsim
2013-Dec-05, 08:35 AM
If "they might not be there" is really the best thing you can come up with, I'm going to be very disappointed.Hmmphff! ...

I thought it was quite an elegant refutation myself ... :)

Noclevername
2013-Dec-05, 12:59 PM
Hmmphff! ...

I thought it was quite an elegant refutation myself ... :)

Then I failed to communicate my intent clearly enough. Provide a convincing argument that they can't be there. :)

marsbug
2013-Dec-05, 02:03 PM
For me that's a tall order: Yes water under those conditions is very different from the liquid we're used to, but liquid methane and ethane are both very different liquids than water, and there's still been no absloute refutation (that I've heard of) of the possibility of life existing in those. I think many of the same arguments would apply: Boiling down to 'we can't say it couldn't happen, we can speculate to some depth on how it might / might not work, but we can be sure that it would be very very different, and hard to identify.

Noclevername
2013-Dec-06, 01:45 AM
Well, I'd settle for a partial refutation, explaining why it's unlikely they're there.

Selfsim
2013-Dec-06, 02:26 AM
Then I failed to communicate my intent clearly enough. Provide a convincing argument that they can't be there. :)So if you don't get a convincing argument, then you can conclude: "its unknown"! Cool!
(Didn't really need to ask the question at all then, eh?)

Noclevername
2013-Dec-06, 03:32 AM
I have very little knowledge of what sort of chemistries could function at such pressures and temperatures. http://en.wikipedia.org/wiki/Supercritical_fluid
WP says:
Supercritical water can be used to decompose biomass via supercritical water gasification of biomass[11] This type of biomass gasification can be used to produce hydrocarbon fuels for use in an efficient combustion device or to produce hydrogen for use in a fuel cell. In the latter case, hydrogen yield can be much higher than the hydrogen content of the biomass due to steam reforming where water is a hydrogen-providing participant in the overall reaction.

So traditional organics will not behave in at all the same way. But:


Nano and micro particle formation

The formation of small particles of a substance with a narrow size distribution is an important process in the pharmaceutical and other industries. Supercritical fluids provide a number of ways of achieving this by rapidly exceeding the saturation point of a solute by dilution, depressurization or a combination of these. These processes occur faster in supercritical fluids than in liquids, promoting nucleation or spinodal decomposition over crystal growth and yielding very small and regularly sized particles. Recent supercritical fluids have shown the capability to reduce particles up to a range of 5-2000 nm.[16]

and

Supercritical fluids act as a new media for the generation of novel crystalline forms of APIs (Active Pharmaceutical Ingredients) named as pharmaceutical cocrystals. Supercritical fluid technology offers a new platform that allows a single-step generation of particles that are difficult or even impossible to obtain by traditional techniques. The generation of pure and dried new cocrystals (crystalline molecular complexes comprising the API and one or more conformers in the crystal lattice) can be achieved due to unique properties of SCFs by using different supercritical fluid properties: supercritical CO2 solvent power, anti-solvent effect and its atomization enhancement
as well as

Supercritical fluids can be used to deposit functional nanostructured films and nanometer-size particles of metals onto surfaces. The gas-like surface tension, diffusivities, and viscosities allows access to nano pores much smaller than can be accessed by liquids, and the liquid-like solubilities allow much higher precursor concentrations than are typical in chemical vapour deposition.[31] This is crucial in developing more powerful electronic components, and metal particles deposited in this way are also powerful catalysts for chemical synthesis and electrochemical reactions.

So clearly very complex chemistry can be at work under such conditions.

What maximum pressures and temperatures of water and other volatiles have been achieved in the lab?

Noclevername
2013-Dec-06, 10:52 AM
Since the properties of supercritical fluids vary by pressure, I can picture a stratified ecosystem, with the types of life, and even the chemical makeup, varying radically by depth. There could be two "civilized" intelligent species who can become aware of each other and communicate by sound, but be separated by layers of water neither can cross.

ravens_cry
2013-Dec-06, 06:42 PM
Since the properties of supercritical fluids vary by pressure, I can picture a stratified ecosystem, with the types of life, and even the chemical makeup, varying radically by depth. There could be two "civilized" intelligent species who can become aware of each other and communicate by sound, but be separated by layers of water neither can cross.
And so cobble together some interlayer craft capable of crossing the boundary between their worlds. I think it could make a pretty thrilling story, like "Surface Tension" by James Blish mixed with "A Meeting with Medusa" by Arthur C. Clarke.
***
Funny aside, I was making sure I got the name right by googling "meeting with medusa" when Google's little event calendar popped up with "Create event
11:00 AM – 11:30 AM
Meeting with medusa"
I don't know about anyone else, but that made me chuckle.

KaiYeves
2013-Dec-06, 06:56 PM
And so cobble together some interlayer craft capable of crossing the boundary between their worlds. I think it could make a pretty thrilling story, like "Surface Tension" by James Blish mixed with "A Meeting with Medusa" by Arthur C. Clarke.
***
Funny aside, I was making sure I got the name right by googling "meeting with medusa" when Google's little event calendar popped up with "Create event
11:00 AM – 11:30 AM
Meeting with medusa"
I don't know about anyone else, but that made me chuckle.

"Meeting with Medusa, 11:00-11:30 AM, wear shades, bring mirror."

ravens_cry
2013-Dec-06, 07:18 PM
"Meeting with Medusa, 11:00-11:30 AM, wear shades, bring mirror."
Then you had to cancel the next appointment because you got stoned.:D

KaiYeves
2013-Dec-06, 09:41 PM
Then you had to cancel the next appointment because you got stoned.:D

Not if I wear welding goggles and hold up the mirror...

Noclevername
2013-Dec-06, 11:06 PM
Dragging the conversation back on topic, kicking and screaming:

It's possible that a Neptunian or Uranian lifeform could use this as a hunting method; it produces a pressure burst, the SC fluid changes state around them, their prey's molecular nanostructure locks up, and the prey's body becomes an inflexible solid! Supercritical fluids are whacky things.

ravens_cry
2013-Dec-06, 11:30 PM
Dragging the conversation back on topic, kicking and screaming:

It's possible that a Neptunian or Uranian lifeform could use this as a hunting method; it produces a pressure burst, the SC fluid changes state around them, their prey's molecular nanostructure locks up, and the prey's body becomes an inflexible solid! Supercritical fluids are whacky things.
Given the crazy tactics we see here on Earth, like the 'super cavitation shock wave'* of the pistol shrimp, I wouldn't be surprised at all.
*Now don't that sound like something from a bad anime?

Noclevername
2013-Dec-06, 11:39 PM
Yay, I accidentally gave a plausible example! :razz:

ravens_cry
2013-Dec-07, 07:02 AM
Yay, I accidentally gave a plausible example! :razz:
To be honest, you are talking to the wrong person whether that's plausible or not, I just though it sounded cool and no weirder than some of the strategies of our fellow travellers on Starship Earth.

Colin Robinson
2013-Dec-08, 02:07 AM
Now, I'm not talking about its moons (http://cosmoquest.org/forum/showthread.php?147749-Ice-is-nice-but-Water-is-wetter), but the inside of the planet Neptune and its poor cousin, Uranus. Both are considered to be "ice giants" because they are thought to contain vast quantities of H2O and other volatiles.
Now from my layman's understanding, the ice under those massive pressures is not frozen at all, but some kind of ultra-dense hot super-ice. And I am given to believe that there may be some kind of ultra-dense super-water may also exist at certain depths within those worlds.
A question to consider is whether water (as distinct from ice) can exist in those ultra-dense conditions? Or some other fluid that could perform the same sort of role in a Neptunian biology as water performs here on Earth?

Higher up the atmosphere it would not be so ultra-dense. Conceivably droplets of fluid exist at particular levels of the atmosphere, but not at the level where the environment consists of solids rather than gases. Just as there are droplets of H2SO4 in the clouds of Venus but not at the surface.

But then there is the question mentioned by TheBrett…

If I remember right, there used to be proposals that some type of life could emerge in Jupiter's atmosphere, but that mostly faded away because we discovered weather patterns that sucked parts of the atmosphere down deep - the kind of change that would kill just about any life we would recognize.
If it is accepted that the gas giants have weather patterns which sweep stuff deep down, then the question to consider is whether any system involving complex chemical compounds and fluid solvents could survive the temperatures and pressures they’d encounter in those deep down levels of the atmosphere?

So we get back to question of what can and can’t happen in ultra-dense conditions…

Noclevername
2013-Dec-08, 02:36 AM
If it is accepted that the gas giants have weather patterns which sweep stuff deep down, then the question to consider is whether any system involving complex chemical compounds and fluid solvents could survive the temperatures and pressures they’d encounter in those deep down levels of the atmosphere?


But the weather patterns of Neptune are totally different from those of Jupiter. It's cooler both from less internal heating and less solar heating, and its composition is different, so it experiences far less massive storms. Uranus is only slightly less quiescent than Neptune.

http://en.wikipedia.org/wiki/Ice_giant:
An ice giant is a type of giant planet composed largely of materials less volatile than hydrogen and helium.[1] It became known in the 1990s that Uranus and Neptune were really a distinct class of giant planet, composed of about 20% hydrogen, compared to the heavier gas giant's 90%.[1] They are primarily composed of 'ices'—volatile elements heavier than hydrogen and helium.[1] These materials were actually ices during the ice giants' formation, but now they exist in different phases, primarily supercritical fluids.[1] The 'ice' is primarily  H2O and is generally treated as such, making the equation of state of water important for modeling ice giants.[2] Ice giants are thought to lack metallic hydrogen at their cores, unlike the gas giants.


Their magnetic fields are believed to originate in an ionized convecting molten ice mantle.

Grant Hatch
2013-Dec-08, 05:26 AM
I'm pretty sure I might have possibly had an out of body astral projection experience while dreaming...., where I am pretty sure I was high up in the atmosphere of a planet fairly close to earth and where I saw large jellyfish/zeppelin like critters floating about in the clouds (beautifully colored and lit by the way,... the clouds not the critters) above an increasingly dark/dense and forbidding environment below me ......... I decided it was Jupiter but... could have been one of the others.....well, it was just a dream.....after all. How's that for proof!

Seriously, I'd be flabbergasted if we do not find life elsewhere in the solar system. Complexity and all.... really, what makes our planet so special? Just because we have an environment that is not reflected elsewhere in the solar system doesn't mean we have the only one that will support "life". Extremophiles are pointing the way.... There's more than one way to make an omelet.

Noclevername
2013-Dec-08, 08:26 AM
How's that for proof!


I'm looking for disproof, though. Or at least practical discouragement based on physical properties.

Spacedude
2013-Dec-08, 03:48 PM
Sorry Nocleavername (That's fairly cleaver enough :), but you'll get no argument from me on this.
I tend to keep the life formula simple : Physics evolved into Chemistry which evolved into Biology...

Fluid + Energy + Time = Life

To us, the Earth was nothing but a toxic waste dump 3 billion years ago and yet it was teaming with microbes.

Noclevername
2013-Dec-08, 05:09 PM
*Sigh* Where's your "A" game, people? I'm not getting the sense that anyone's seriously trying to raise valid objections based on physical laws.

I'm almost tempted to ask to have this thread moved into ATM, and claim the possibility as my hypothesis. But for now, I'll keep it here and hope.

marsbug
2013-Dec-08, 11:30 PM
I really genuinely can't think of a fundamental objection to, um, life that uses water as its biosolvent. I might go so far as to say I'd feel slightly hypocritical if I had any such objections.

I just spent my sunday afternoon teaching trigonometry, give me a break ok? :p

Noclevername
2013-Dec-09, 12:38 AM
I really genuinely can't think of a fundamental objection to, um, life that uses water as its biosolvent.


But supercritical water is an extremely different beast than liquid water. I'm asking about the conditions that would exist inside a totally alien environment compared to the surface of Earth.

marsbug
2013-Dec-09, 12:12 PM
Ok: Supercritical water is known to dissolve non polar compounds far more effectively than regular water, making forming a stable cell harder. Its 600 K odd critical temp also suggests to me that a lot of organic compounds wouldn't hold together in it. I found a few tidbits and a few references on the subject here (http://books.nap.edu/openbook.php?record_id=11919&page=78), and I'll do some more reading to better inform my objections as soon as I've got some time (promise).

Noclevername
2013-Dec-09, 12:15 PM
Ok: Supercritical water is known to dissolve non polar compounds far more effectively than regular water, making forming a stable cell harder. Its 600 K odd critical temp also suggests to me that a lot of organic compounds wouldn't hold together in it. I found a few tidbits and a few references on the subject here (http://books.nap.edu/openbook.php?record_id=11919&page=78), and I'll do some more reading to better inform my objections as soon as I've got some time (promise).

Thank you. I appreciate that you're making the effort.

marsbug
2013-Dec-09, 12:28 PM
Organic chemistry in supercritical water really isn't my thing, but it's a great idea to help explore the popssibility of neptunians, and it sure as hell beats re-hashing the 'what is the definition life' or 'could microbes have reached/left Earth via meteorite' arguments for the nth time. If you had an organic chemist ready to debate with you I'd keep clear, but since you haven't at least I can try and help you get it started.

Noclevername
2013-Dec-09, 04:09 PM
Organic chemistry in supercritical water really isn't my thing, but it's a great idea to help explore the popssibility of neptunians, and it sure as hell beats re-hashing the 'what is the definition life' or 'could microbes have reached/left Earth via meteorite' arguments for the nth time. If you had an organic chemist ready to debate with you I'd keep clear, but since you haven't at least I can try and help you get it started.

Thanks. (And yeah, I agree about the "same old arguments". It gets a bit old.)

I like that description "molten ice" WP uses to refer to the interior of giant planets, it conveys a feel for the conditions there and carries its own connotations.

marsbug
2013-Dec-11, 01:12 PM
I think my main objection is going to be that, under the hypothesised conditions of the water-ammonia mantle, the kind of organic chemistry that life depends on just can't happen. I know quoteing wikipedia is a frowned upon thing, but it's summation of conditions in the ocean bears quoting here I think:


The mantle reaches temperatures of 2,000 K to 5,000 K. It is equivalent to 10 to 15 Earth masses and is rich in water, ammonia and methane.[1] As is customary in planetary science, this mixture is referred to as icy even though it is a hot, highly dense fluid. This fluid, which has a high electrical conductivity, is sometimes called a water–ammonia ocean.[44] At a depth of 7000 km, the conditions may be such that methane decomposes into diamond crystals that then precipitate toward the core.[45] The mantle may consist of a layer of ionic water where the water molecules break down into a soup of hydrogen and oxygen ions, and deeper down superionic water in which the oxygen crystallises but the hydrogen ions float around freely within the oxygen lattice.[46] (http://en.wikipedia.org/wiki/Neptune#Internal_structure)

So even the description of 'molten ice' is only apt for the uppermost layers. Below them we have layers that sound vaugely like a kind of high density plasma, and below that crystalline oxygen swarming with free protons. It sounds like an incredible, bizzare, fascinating place. But any emergent complexity that arises there, and is sufficiently analogous to Earth 'life', would have to be based on principles we can only guess about.

Do you have any specific notions of how a life form might be structured down there? That would give me something specific to try and examine and possibly object to, rather than just handwavily saying 'it's terrible there, what can suirvive in that!?'. For example; what kind of structure (for any of the layers) might exist down there that could carry information on how it itself is made and replicate? I can only imagine something a bit like a diamond snowflake surviving, and that will have very limited scope to evolve into something 'lifelike'....

Noclevername
2013-Dec-11, 01:45 PM
I think my main objection is going to be that, under the hypothesised conditions of the water-ammonia mantle, the kind of organic chemistry that life depends on just can't happen. I know quoteing wikipedia is a frowned upon thing, but it's summation of conditions in the ocean bears quoting here I think:



So even the description of 'molten ice' is only apt for the uppermost layers. Below them we have layers that sound vaugely like a kind of high density plasma, and below that crystalline oxygen crystals swarming with free protons. It sounds like an incredible, bizzare, fascinating place. But any emergent complexity that arises there, and is sufficiently analogous to Earth 'life', would have to be based on principle we can only guess about. For example, what kind of structure do you have in mind (for any of the layers) that could carry information on how it itslef is made and replicate? I can only imagine something a bit like a diamond snowflake survciving, and that will have very limited scope to evolve into something 'lifelike'....

OK, that definitely makes sense.

I wasn't really sure what kind of complex structures could "survive" there. I basically thought that since the WP article on SCF mentioned nanostructures forming under those conditions, it might lead to something self-replicating and thus to life (BTW I quote WP a lot, I had no idea it was frowned on!).

marsbug
2013-Dec-11, 02:24 PM
OK, that definitely makes sense.

I wasn't really sure what kind of complex structures could "survive" there. I basically thought that since the WP article on SCF mentioned nanostructures forming under those conditions, it might lead to something self-replicating and thus to life

Oooh, I din't read that bit yet. Let me have a gander about what kinds of particles can form. I do note that it syas the hottest and deepest underwater volcanoes can produce supercritical water - perhaps there is a realistic scope for seeing what (if anything) might be able to adapt to the lower end of the neptunian spectrum of conditions.


(BTW I quote WP a lot, I had no idea it was frowned on!).

I used to hang out on unmannedspaceflight.com, where if you cite something as evidence it had better be peer reviewed - things are probably still more relaxed here.

marsbug
2013-Dec-11, 02:43 PM
Just off a quick read through before I go and do some christmas shopping: The WP article is talking about industry techniques for producing nanoparticles, and they all seem to use a sudden change in the supercritical fluids composition, pressure, or temperature to accomplish this. So these crystals would not occur in a stable well behaved supercritical ocean, it would need to be turbulent, perhaps to a very high degree. To fulfill even one of the basic properties of life these crystals would then need to migrate to another turbulent zone and somehow influence the growth of nanoscrystals there to have the same internal ordering as the original crystals - so there would need to be a plausible mechanism for that, and the WP description makes it sound like nanocrystal composition is down to the composition of the fluid, rather than a seeding crystal. I know that in crystal growth seeded in a supersaturated fluid from a seeding crystal the daughter crystals can 'inherit' some of the internal structure of the seed crystal, but the production of the nanoparticles doersn't sound very anolagous to that.

But I was only skimming - anyone else want to chime in.?

Noclevername
2013-Dec-15, 12:04 PM
Just off a quick read through before I go and do some christmas shopping: The WP article is talking about industry techniques for producing nanoparticles, and they all seem to use a sudden change in the supercritical fluids composition, pressure, or temperature to accomplish this. So these crystals would not occur in a stable well behaved supercritical ocean, it would need to be turbulent, perhaps to a very high degree. To fulfill even one of the basic properties of life these crystals would then need to migrate to another turbulent zone and somehow influence the growth of nanoscrystals there to have the same internal ordering as the original crystals - so there would need to be a plausible mechanism for that, and the WP description makes it sound like nanocrystal composition is down to the composition of the fluid, rather than a seeding crystal. I know that in crystal growth seeded in a supersaturated fluid from a seeding crystal the daughter crystals can 'inherit' some of the internal structure of the seed crystal, but the production of the nanoparticles doersn't sound very anolagous to that.

But I was only skimming - anyone else want to chime in.?

There could be shifts in pressure if some form of internal "volcanism" between layers takes place, or currents churn up the "magma" of molten ice. I just don't know enough about high-pressure physics to say if these shifts could be radical enough or take place fast enough to produce the kinds of complex structures needed for replication, or if they could survive the very conditions that would create them.

marsbug
2013-Dec-15, 01:34 PM
The 'ocean' of Neptune is known only through modles, but we do have some hard data on the atmosphere above it, so i'd start with that: The atmosphere of Neptune may contain a water cloud layer at pressures over 50bars (where the temperature is thought to rise above 273 kelvin), much as the atmospheres of the other giant/ice giant planets are thought to. Above this are thought to be cloud layers containing ammonia, which has a lower freezing point than water and is also often bandied around as being a possible biosolvent (as in many ways it is similar to water). It also has methane, exposed to solar and cosmic radiation which could cause it to polymerise into tholins and other biological precursors. So we have clouds of liquid droplets of biosolvents, a possible source of long chain carbon molecules, and heat energy. If the water cloud layer is fasirly stable, could the above give us some play to speculate about airborne micro-organisms evolving (as was once suggested for Jupiter)?

These might then evolve to survive in the lower atmospheric layers, eventually reaching the 'ocean' without the need for conditions that would form self replicating nano particles. Very handwavy and speculative but that's the most likely scenario for neptunian life (barring it being introduced in some highly engineered form from Earth one day) that I can come up with. like you, I'm unable to really tackle the idea of life arising in the ocean from scratch as I don't have the understanding of ultra high pressure physics, and humankind does not have any hard data on what is actually happening down there.

Noclevername
2013-Dec-15, 02:24 PM
The 'ocean' of Neptune is known only through modles, but we do have some hard data on the atmosphere above it, so i'd start with that: The atmosphere of Neptune may contain a water cloud layer at pressures over 50bars (where the temperature is thought to rise above 273 kelvin), much as the atmospheres of the other giant/ice giant planets are thought to. Above this are thought to be cloud layers containing ammonia, which has a lower freezing point than water and is also often bandied around as being a possible biosolvent (as in many ways it is similar to water). It also has methane, exposed to solar and cosmic radiation which could cause it to polymerise into tholins and other biological precursors. So we have clouds of liquid droplets of biosolvents, a possible source of long chain carbon molecules, and heat energy. If the water cloud layer is fasirly stable, could the above give us some play to speculate about airborne micro-organisms evolving (as was once suggested for Jupiter)?

These might then evolve to survive in the lower atmospheric layers, eventually reaching the 'ocean' without the need for conditions that would form self replicating nano particles. Very handwavy and speculative but that's the most likely scenario for neptunian life (barring it being introduced in some highly engineered form from Earth one day) that I can come up with. like you, I'm unable to really tackle the idea of life arising in the ocean from scratch as I don't have the understanding of ultra high pressure physics, and humankind does not have any hard data on what is actually happening down there.

I hadn't really given much thought to life developing in the outer layers, but it sounds like more of a possibility than some more exotic life forming under the much more difficult conditions of the ice-9 underlayers.

If it turns out someday there is some "meat" to this idea, then it would have interesting implications for exolife; we sun-lit ground-walkers might be outnumbered by ice-giant flyers and ice-moon swimmers! :D

Noclevername
2013-Dec-15, 02:45 PM
If it turns out someday there is some "meat" to this idea, then it would have interesting implications for exolife; we sun-lit ground-walkers might be outnumbered by ice-giant flyers and ice-moon swimmers! :D

HUMAN: "Hey, this starship doesn't have any legroom and the lights don't work!"

ET: "Perfect, we'll take it!"

TheBrett
2013-Dec-18, 06:16 PM
I wonder if we could drop a "diving bell"-style probe that would be "buoyant" in Neptune's lower atmosphere at certain air pressures. I know there are proposals for putting something in Venus's atmosphere that would float at a certain air density.

50 bar pressure by itself is something we can work with - it's the equivalent of going 490 meters down in the ocean in terms of depth. Whales dive deeper than that.

marsbug
2013-Dec-19, 10:55 AM
Definitely, and in an ideal solar system we should! The problem is getting it out to Neptune on a budget - any Neptune mission other than a fast flyby needs heinous amounts of gas.

IsaacKuo
2013-Dec-19, 09:13 PM
Definitely, and in an ideal solar system we should! The problem is getting it out to Neptune on a budget - any Neptune mission other than a fast flyby needs heinous amounts of gas.
Not if you use Neptune's atmosphere to brake. While aerocapture is, as yet, an unused technique, direct atmospheric entry has been done.

The actual delta-v requirements to get to Neptune are the same as what's required to reach Jupiter. If you can reach Jupiter at all, you can get a free gravity assist to Neptune. And, in fact, the gravity assist windows to Neptune are more frequent than the gravity assist windows to Saturn (about once every 12 years, vs about once every 2 decades).

marsbug
2013-Dec-20, 12:45 AM
True, I was thinking of a straight up Hohman transfer orbit, which is both unimaginative and making lots of needless hard work (and I hate that). To drop a direct probe into the atmosphere we are still looking at something akin to the Galileo probe. That survived to a pressure of 23 atmospheres, so I'd say hitting 50 atmospheres depth on Neptune might not be out of the question.

Let us say we have dragged ourselves and our Neptune probe through the selection process, it's gonna happen, and it's planned to reach the water-droplet cloud layer. Once there, what do we want to look for? If we're still thinking of assessing the potential habitability of Neptunian water clouds we'll need to examine the water droplets for microparticles, and biologically relevant molecules....amino acids, or lipids for example. I don't know much about that beyond 'look for carbon compounds'. Raman spectrometers can be made fairly compact, and Raman analysis is fairly insensitive to water IIRC....?

Bacteria have been found alive and apparently metabolising in cloud droplets on Earth (link to article (http://www.npr.org/2013/01/29/170459317/bird-plane-bacteria-microbes-thrive-in-storm-clouds) and link to original paper (http://www.pnas.org/content/early/2013/01/22/1212089110)) so it's not utterly outlandish, if the water cloud layer is very stable, to speculate on something simple and rapidly spreading making a living there. Bear in mind I'm not shouting 'the Neptunian cloud creatures LIVEEEE!' from my rooftop here (it's cold tonight) i'm just keeping an open mind on a field I'm no expert on.

The biggest objection I have is that the water droplet layer must somehow have accumulated sufficient useable carbon compounds for organisms to use, and must stay as stable as a big herd of sleeping horses. And my biggest objection to finding them (if they are there) is the use of aerocapture to brake at Neptune. As far as I know it has only been tried fro a few of the Zond missions, on lunar return trajectories. It's entirely unproven on an interplanetary mission - so we'll need to find funding for a few cheap-o demonstration missions for aerocapture at the relevant speeds, before we even think about asking for funding for the big mission to Neptune.

IsaacKuo
2013-Dec-20, 02:12 AM
To drop a direct probe into the atmosphere we are still looking at something akin to the Galileo probe. That survived to a pressure of 23 atmospheres, so I'd say hitting 50 atmospheres depth on Neptune might not be out of the question.
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And my biggest objection to finding them (if they are there) is the use of aerocapture to brake at Neptune. As far as I know it has only been tried fro a few of the Zond missions, on lunar return trajectories. It's entirely unproven on an interplanetary mission - so we'll need to find funding for a few cheap-o demonstration missions for aerocapture at the relevant speeds, before we even think about asking for funding for the big mission to Neptune.
Actually, direct atmospheric entry to Neptune would be at much lower entry speed than the Galileo probe. The Galileo probe hit Jupiter's atmosphere at over 47km/s (the minimum possible entry speed would have been 42km/s, the lowest possible orbital speed). In contrast, escape velocity from Neptune is only 23.5km/s. An atmospheric entry probe directly plunging into Neptune's atmosphere from an interplanetary trajectory would hit Neptune's atmosphere at around 24 or 25 km/s.

Basically, experience from the Galileo atmospheric entry probe is directly applicable to a Neptune atmospheric entry probe. The heat shield could be made a millimeter or so thinner, to account for the much lower entry speed, with the rest of the design essentially unchanged (the hydrogen atmosphere composition is much the same; the atmospheric composition determines the ideal heat shield cone angle).

BTW, aerocapture generally refers to a different maneuver than atmospheric entry--it is an as yet untried technique to use atmospheric drag to reduce speed from a hyperbolic interplanetary trajectory to an elliptical orbit. This maneuver is related to aerobraking and atmospheric entry, but it is more technically challenging than either. Aerocapture requires very good certainty on atmospheric drag at relevant altitudes. Too little drag, and the spacecraft will fail to reduce speed below escape velocity--it will go sailing off into interplanetary space rather than the intended orbit around the target planet. Too much drag, and the spacecraft will reduce speed below orbital velocity, resulting in undesired atmospheric entry rather than orbit around the target planet. An atmospheric entry maneuver can conservatively guess in the direction of applying too much drag. An aerobraking maneuver can conservatively guess in the direction of applying too little drag. An aerocapture maneuver has to thread things just right.

marsbug
2013-Dec-20, 02:31 AM
I'm still thinking about an aerocapture (in spite of your cool explanation) as I expect we will still need an orbiter to relay the atmospheric probe's signal back to Earth. I totally get that the atmosphere probe is doing an atmospheric entry, but unless we give it a transmitter strong enough to punch through miles of atmosphere and cloud and still have enough power to be received on Earth (which would make it bigger and heavier and hence all around a more difficult thing to do) won't we need at least a basic orbiter to act as a relay station? How would we get the atmospheric data needed to pull an aerocapture off?

Or am I overestimating the power needed for a standalone atmosphere probe to send a signal home?

IsaacKuo
2013-Dec-20, 05:01 PM
I'm still thinking about an aerocapture (in spite of your cool explanation) as I expect we will still need an orbiter to relay the atmospheric probe's signal back to Earth. I totally get that the atmosphere probe is doing an atmospheric entry, but unless we give it a transmitter strong enough to punch through miles of atmosphere and cloud and still have enough power to be received on Earth (which would make it bigger and heavier and hence all around a more difficult thing to do) won't we need at least a basic orbiter to act as a relay station? How would we get the atmospheric data needed to pull an aerocapture off?

Or am I overestimating the power needed for a standalone atmosphere probe to send a signal home?

Honestly, splitting the mission up into an orbiter and an atmospheric entry probe makes more sense anyway. Depending on how turbulent the flight is, it may be problematic to point an antenna dish back home. And an independent orbiter can gather a lot of useful data on Neptune and its system in its own right.

But aerocapture is still not really such a good idea compared to traditional powered insertion and then aerobraking. It only takes 525m/s delta-v to do powered insertion from a hyperbolic excess velocity of 5km/s. That's the power of the Oberth effect. From this elliptical orbit, aerobraking can be used to lower the orbit into a more circular orbit (perhaps one more suitable for studying Triton).

Assuming the orbiter's maneuver thrusters have a specific impulse around 300s, 525m/s delta-v only costs a mass penalty of an extra 20% in propellant. A suitable heat shield for aerocapture could incur a similar mass penalty, while also adding technology risk. (Note that aerobraking does not require a heat shield. It gently brakes the spacecraft by relatively small amounts over multiple orbits.)

marsbug
2013-Dec-20, 05:45 PM
Thanks Issac, I get the feeling you've had thoughts along this Neptunian line before now? It sounds more do-able than I'd expected... Even a Neptune orbiter, sans atmosphere probe, could tell us a lot. I think JUNO has an instrument that will use microwave frequencies to map the Jovian water cloud layer from orbit (shakes fist at ye dark and capricous gods of budgets). I wonder if a private concern might be persuaded to launch a modest probe Neptune's way?

WRT what could be happening in the supercritical ocean, this article from sciencedaily (http://www.sciencedaily.com/releases/2013/12/131219142138.htm) suggests to me it might be something of a natural laboratory for exotic chemistry - well worth the effort to investigate if we ever can, given how nature always seems to find things we couldn't have dreamed of...


His discovery may have application in the planetary sciences, where high-pressure phenomena abound. It may explain results of other experiments, where researchers compressed materials and got puzzling results. His computational methodology and structure-prediction algorithms will help researchers predict material combinations and structures that exhibit desired properties and levels of stability.

"We have learned an important lesson -- that even in well-defined systems, like sodium chloride, you can find totally new chemistry, and totally new and very exciting materials," Oganov says. "It's like discovering a new continent; now we need to map the land. Current rules cannot cope with this new chemistry. We need to invent something that will."

IsaacKuo
2013-Dec-20, 10:18 PM
I've actually not really put any thought into a Neptune mission. I'm able to pontificate on the orbital mechanics, because the orbital mechanics involved are much the same as Saturn missions--which I have looked at more thoroughly. The big difference is distance. Because Neptune is so far away, a minimum delta-v Hohmann transfer orbit from Jupiter to Neptune is out of the question. This would require a travel time of about 4 decades. As such, any practical mission will be a compromise between travel time and delta-v requirement at Neptune.

Now, maybe I missed something...is there some particular reason you'd rather send this mission to Neptune than Uranus? Uranus is rather interesting itself for many reasons, and an orbiter could be awesome for studying its bizarre magnetic field.

The minimum delta-v requirements for a Uranus mission and Neptune mission would be similar, but the travel time to Uranus at minimum delta-v would only be about 2 decades.

marsbug
2013-Dec-20, 11:02 PM
No great preference for Neptune over Uranus, just following on from the OP that raised the question of life in the Neptunian (as opposed Uranian) supercritical 'ocean'.

Noclevername
2013-Dec-20, 11:07 PM
I have no particular planetary preference. But IIRC Uranus is more churned up, meaning its atmospheric conditions may be less stable and less conducive to life.

Colin Robinson
2013-Dec-21, 10:07 PM
Ok: Supercritical water is known to dissolve non polar compounds far more effectively than regular water, making forming a stable cell harder.

If we consider any solvent other than the form of liquid water familiar on Earth's surface, it is likely to be either a stronger solvent or a weaker solvent, and to dissolve a different set of substances. This means that you couldn't simply take a terrestrial water-based organism, replace its liquid water with something else (such as supercritical water), and expect it to function.

The question is whether there are any substances which supercritical water does not dissolve, and which could occur and persist in Neptune conditions? If there are, is it conceivable that cell-like structures could be formed of those substances?

marsbug
2013-Dec-22, 05:24 PM
Sorry for the delay replying. The more I read the harder it is to get an idea of what could be stable down there! But most of what I've found is about using SC H2O to destroy organic compounds, which it seems to be very effective at. So our hypothetical cell wall may need to be inorganic, which raises the question of where do we get inorganic compounds from - Neptune and Uranus are thought to have silicate/ metal cores but we need something that will form compartments, and we need it in the 'ocean', not the core...

Noclevername
2013-Dec-22, 05:43 PM
WRT the plants, I was basically just going for the whole ocean/Sea God connection, hence Neptune. Also wanted to avoid the "probe Uranus" jokes.

Physically, though, Uranus has less internal heat and more turbulence. Its atmosphere composition also seems to have less hydrocarbons than Neptune, that's possibly why the color is lighter.

ravens_cry
2013-Dec-22, 08:42 PM
I think some Antarctic fish have to deal with supercritical conditions, like bottom feeding icefish, lacking many of the anti-freeze proteins of many Antarctic fish, must avoid contact with ice, or they can freeze solid.

marsbug
2013-Dec-23, 07:16 PM
Do you mean supercooled (water cooled below freezing)? The critical point for water is 374 degrees celcius-ish, which would be ice free, but give a fish a fair bit else to worry about. Probably very briefly.

ravens_cry
2013-Dec-23, 08:53 PM
Do you mean supercooled (water cooled below freezing)? The critical point for water is 374 degrees celcius-ish, which would be ice free, but give a fish a fair bit else to worry about. Probably very briefly.

Oh yes, my bad. Yes, would be a very brief worry. They might even get . . . steamed.

marsbug
2013-Dec-23, 09:28 PM
:D Boom Boom Tssk :D

marsbug
2013-Dec-24, 09:12 PM
Early Christmas present to all would be Neptunians: http://arxiv.org/abs/1312.6554

Not just an atmospheric probe mission, but using a novel type of engine to...

litespeed
2014-Jan-01, 09:43 AM
I also think Neptune and Uranus moons are the way to go if we ( in the future ) go manned space flites 5-10 times faster than Cassini -Huygens at present speed does.

Noclevername
2014-Jan-01, 05:58 PM
I also think Neptune and Uranus moons are the way to go if we ( in the future ) go manned space flites 5-10 times faster than Cassini -Huygens at present speed does.

Welcome, litespeed.

Although the outer planets' moons are a fascinating topic themselves, this thread's actually about the interior of the planets.

Hlafordlaes
2014-Jan-03, 11:56 PM
Dragging the conversation back on topic, kicking and screaming:

It's possible that a Neptunian or Uranian lifeform could use this as a hunting method; it produces a pressure burst, the SC fluid changes state around them, their prey's molecular nanostructure locks up, and the prey's body becomes an inflexible solid! Supercritical fluids are whacky things.

Can't comment on the chemistry or plausibility, but you got yourself a decent sci-fi short story premise right there. Stephen-Baxterish, perhaps.

ashtaroth
2014-May-28, 10:49 AM
main condition for any life forming is a liquid like space to form. so therefore...

primummobile
2014-May-29, 04:23 PM
main condition for any life forming is a liquid like space to form. so therefore...

A condition for any Earth-like life to form is the availability of a liquid solvent.

Noclevername
2014-May-29, 04:35 PM
Welcome, ashtaroth.